Japanese Patent Application 51348/65 discloses the preparation of methacryloyloxyalkylalkoxysilanes and acryloyloxyalkylalkoxysilanes from alkali metal methacrylates or acrylates and chloroalkylalkoxysilanes, using quaternary ammonium salts as solid/liquid phase transfer catalysts. The reaction temperatures given in this publication are 140.degree. to 180.degree. C. However, according to C. M. Starks and C. Liotta (Phase Transfer Catalysis, Academic Press, New York 1978, page 64), ammonium salts rapidly lose their activity above 110.degree. to 120.degree. C. This explains the low yields of the process described in the Japanese Application. As a result of the thermal decomposition of the quaternary ammonium salts in the presence of alkali metal methacrylates or acrylates, tertiary amines and alkyl methacrylates or acrylates are formed as by-products and, because of similar boiling points, are difficult to separate from methacryloyloxyalkylalkoxysilanes or acryloyloxyalkylalkoxysilanes by distillation.
Methacryloyloxyalkylalkoxysilanes and acryloyloxyalkylalkoxysilanes are frequently used as adhesion promoters in sizes for glass fibers and also as industrially interesting comonomers for the production of sealing compounds and moisture-curable coating systems, for example. However, it is well known by those skilled in the art that high purity is required for industrial use of these methacryloyloxyalkylalkoxysilanes or acryloyloxyalkylalkoxysilanes, for example in sizes for glass fibers or in polymerization reactions.